TEMPERATURE DEPENDENCES OF AIR-BROADENING AND SHIFT

PARAMETERS IN THE ν3 BAND OF OZONE

M. A. H. SMITHNASA Langley Research Center, Hampton, VA 23681-2199 U.S.A.

V. MALATHY DEVI and D. CHRIS BENNERThe College of William and Mary, Williamsburg, VA 23187-8795 U.S.A.

RF08 – 70th International Symposium on Molecular Spectroscopy, June 22-26, 2015

Why do we need to know the temperature dependences of spectroscopic line parameters?

Tropopause temperatures vary with latitude and season, and are typically below 195 K in the tropics.

Global Average Temperature Profile

Uncertainties in spectroscopic line parameters propagate into retrievals of atmospheric ozone concentrations.

Change in retrieved atmospheric O3 mixing ratio as a function of altitude for a 60% increase in the assumed air-broadened halfwidth [Smith and Gordley, 1983].

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Present Work: Analyze air-broadened O3 spectra recorded at 160-300K to determine temperature dependences of ν3 air-broadening and shift parameters needed for atmospheric retrievals. ►

T = 297 K, p = 110 torr, VMR = 0.4%, L = 50 cm

used forcalibration

Air-broadened O3 line parameters and their temperature dependences (175–300 K) in the 9.6 µm region are needed for quantitative analysis of spectroscopic observations of Earth’s atmosphere, both to retrieve ozone abundances and to model the O3 absorption overlapping features of other species.

Previous lab T-dependence studies have involved mostly B-type bands: Rotational [Larsen et al., 2001], ν1 [Smith et al., 1997] and ν2 [Malathy Devi et al., 1997].

However, ν3 is A-type!• One study of N2-broadening for 21 ν3 transitions (180-296K) [Spencer et al., 1992].• Air-broadened widths and shifts for 9 ν3 R-branch transitions are included in the

[Smith et al., 1997] ν1 results (210-302K).• [Wagner et al., 2002] reported polynomial representations for ν3 N2- and O2-

broadened widths and temperature dependences (200-298K), but no shifts.

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Lab Spectra Used for Ozone Fits in the ν3 Band

NO. OF DATE SAMPLE VMR TEMPERATURE PRESSURE PATH BAND RES.

SPECTRA (%) (K) (TORR) (m) PASS (cm-1)

2 10-Nov-94 O3 + Air 4.7 300 101, 204 0.0998 2 0.00272 10-Nov-94 O3 + Air 3.6 300 76, 153 0.0998 2 0.00274 7-Feb-96 O3 81 - 90 300 0.3 - 0.5 0.0998 2 0.00271 29-Apr-97 O3 30.3 298 1.3 0.500 2 0.00522 30-Apr-97 O3 + Air 0.6 297 110, 201 0.500 2 0.00523 1-May-97 O3 + Air 0.5 272 101 - 220 0.500 1 0.00523 2-May-97 O3 + Air 0.4 254 107 - 216 0.500 1 0.00523 4-May-97 O3 + Air 0.3 233 104 - 220 0.500 1 0.00525 6-May-97 O3 + Air 0.3 213 86 - 201 0.500 1 0.00521 21-May-98 O3 13 170 2.2 0.095 1 0.0053 21-May-98 O3 + Air 1.5 186 94 - 193 0.095 1 0.0051 22-May-98 O3 + Air 1.9 160 203 0.095 2 0.0051 22-May-98 O3 + Air 1.9 168 134 0.095 2 0.005

Band pass 1 = 500-1400 cm-1; Band pass 2 = 800-1400 cm-1

All spectra were recorded using the McMath-Pierce FTS with KCl beam splitter, 8 mm aperture, and He-cooled As:Si detectors.

February 1996 spectra were used in the previous intensity study [Smith et al., 2001].May 1998 spectra were recorded using a single detector.

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Analysis

Nonlinear least squares multispectrum fitting [Benner et al., 1995] is used to retrieve spectroscopic parameters consistent with the entire set of laboratory spectra.

Voigt line shape is assumed; line mixing is allowed for pairs of lines expected to mix (no mixing observed in intervals fit to date).

All spectra are calibrated to the same wavenumber scale with reference to H2O ν2 line positions.

Room-temperature spectra are fit first; then the lower-temperature spectra are added sequentially down to 213 K.

Noisy spectra from 186 to 160 K are added to the fit last with low weights (poor Signal-to-Noise Ratio due to single detector).

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Example Fit of Air- and Self-Broadened O3 Spectra

A total of 31 spectra were fit.(Standard Deviation of this fit = 0.592%)

These 6 spectra were selected to represent the range of conditions.

Noisy spectra (e.g., 857 and 858) were given lower weights in the fits.

WAVENUMBER (cm-1)

1021.5 1022.0 1022.5

SIG

NAL

0.0

0.2

0.4

0.6

0.8

1.0

Run 702 Run 613Run 794Run 815Run 857 Run 858

1021.5 1022.0 1022.5

RES

IDU

AL

-0.04

-0.02

0.00

0.02

0.04

Run T(Kelvin)

P(torr)

L(cm)

O3 VMR (%)

702 300 0.475 9.98 85.5

613 300 75.5 9.98 3.3

794 233 220 50.0 0.3

815 213 165 50.0 0.3

857 160 202 9.50 1.6

858 170 134 9.50 1.6

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Measured Line Widths and Shifts and Their Temperature Dependences in A-type O3 bands

P-branch lines, J˝ = 15 – 26, Ka˝ = 0 – 11 (● ν3 [Present Work]; ■ ν3 N2-broadening [Spencer et al., 1992]; □ 3ν3 air-broadening [Smith et al., 1994]).

R-branch lines, J˝ = 23 – 36, Ka˝ = 2 – 3, ∆Ka = 2 (○ ν3 air-broadening [Smith et al., 1997]).

Two ν3 transitions with three independent measurements

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Source BroadenerT range (K) Width

Width Tdep Shift Shift Tdep

1021.6451 cm−1 (20,3,18 – 21,3,19)

HITRAN08/12 air 0.0758 0.72 −0.0007

Spencer et al. (1992) N2 180 - 296 0.0751(12) 0.68(6)

Wagner et al. (2002) air (N2, O2) 200 - 296 0.0758 0.721

Present Work air 160 - 300 0.0759(2) 0.660(10) −0.0017(1) 1.8(3)E-051021.8008 cm−1 (18,7,12 – 19,7,13)

HITRAN08/12 air 0.0768 0.72 −0.0007

Spencer et al. (1992) N2 180 - 296 0.0755(14) 0.71(7)

Wagner et al. (2002) air (N2, O2) 200 - 296 0.0768 0.716

Present Work air 160 - 300 0.0778(2) 0.647(16) −0.0018(2) 1.8(5)E-05

Note: Units of Width and Shift are cm-1 atm-1 at 296K, units of Shift Tdep are cm-1 atm-1 K-1, and Width Tdep is unitless. Values in parentheses are 1σ statistical errors in units of the last digit quoted.

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Comparison with Other Fundamentals and Rotational Band

Measured values: ν3 from Present Work, ν2 from [Malathy Devi et al., 1997], ν1 from [Smith et al., 1997] and Rotational from [Larsen et al., 2001].

Calculated values are from empirical formulas given by [Wagner et al., 2002] based on their N2- and O2-broadening measurements at 200 – 298 K.Remember that Rotational, ν1 and ν2 are B-type bands, while ν3 is A-type. Only the lower-state rotational quantum numbers are the same for the transitions compared.

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Measured ν3 air-broadening parameters vs. HITRAN

HITRAN O3 air-broadening and shift parameters are the same in the last three editions [Rothman et al., 2005, 2009, 2013].

◄ (Upper Left) Half widths.

◄ (Lower Left) Temperature dependence exponents of the half widths.

▼ (Below) Pressure-induced line shifts.

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SummaryPresent ν3 results vs. HITRAN

• Measured half widths are 3-5% larger than HITRAN values, especially for transitions with Jʺ < 18.

• Measured n values are up to 15-20% smaller than HITRAN values and have a wider range.

• Measured shift coefficients are mostly larger in magnitude than the constant −0.0007 cm-1 atm-1 HITRAN default value for ν3.

• Shift coefficients with the value 0.0000 are not acceptable (unless measured)!

Future Work Complete the analyses of the laboratory spectra in the entire ν3 band. Provide preliminary results for use in atmospheric retrievals and/or

comparison to calculated widths and shifts. Final results will be included in future spectroscopic database updates (e.g.,

HITRAN).

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Acknowledgements

The research at NASA Langley Research Center, and the College of William and Mary is supported by the Atmospheric Composition Laboratory Research program of the National Aeronautics and Space Administration.

We thank Mike Dulick, Detrick Branston, Claude Plymate and the late Jeremy Wagner of the National Solar Observatory for their assistance in recording the spectra at Kitt Peak over many years. NSO is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under contract with the National Science Foundation.

We especially thank Charles Solomon and Harry Walthall, now retired from the NASA Langley glass shop, for their assistance in the design, construction and testing of the 50 cm coolable cell and the 9.98 cm cell. We are grateful to the late Dr. Charles Chackerian of NASA Ames Research Center for the loan of the 9.5 cm coolable cell.

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References

D. Chris Benner et al., JQSRT 53 (1995) 705-721.R. W. Larsen, F. M. Nicolaisen and G. O. Sørensen, J. Mol. Spectrosc. 210 (2001) 259-270. V. Malathy Devi, D. Chris Benner, M. A. H. Smith and C. P. Rinsland, J. Mol. Spectrosc. 182 (1997) 221-238.L. S. Rothman et al., JQSRT 82 (2003) 5-44.L. S. Rothman et al., JQSRT 96 (2005) 139-204.L. S. Rothman et al., JQSRT 110 (2009) 533-572.L. S. Rothman et al., JQSRT 130 (2013) 4-50.M. A. H. Smith and L. L. Gordley, JQSRT 29 (1983) 413-418.M. A. H. Smith, C. P. Rinsland, V. Malathy Devi and E. S. Prochaska, J. Mol. Spectrosc. 164 (1994) 239-259;

Erratum, J. Mol. Spectrosc. 165 (1994) 596.M. A. H. Smith, V. Malathy Devi, D. Chris Benner and C. P. Rinsland, J. Mol. Spectrosc. 182 (1997) 239-259.M. A. H. Smith, V. Malathy Devi, D. Chris Benner and C. P. Rinsland, J. Geophys. Res. 106 (2001) 9909-9922.M. N. Spencer, C. Chackerian, C. Flannery and J. I. Steinfeld, Spectrochimica Acta 48A (1992) 1273-1282. M. N. Spencer, C. Chackerian, C. Flannery and J. I. Steinfeld, JQSRT 49 (1993) 525-533. G. Wagner, M. Birk, F. Schreier and J.-M. Flaud, J. Geophys. Res. 107 (2002) 4626-4643.